The Mg2NiH4 film on nickel substrate: synthesis, properties and kinetics of formation

• Published in: Thin solid films 2022-11, Vol.762, p.139556, Article 139556
• Main Authors: Baraban, A.P., Chernov, I.A., Dmitriev, V.A., Elets, D.I., Gabis, I.E., Kuznetsov, V.G., Voyt, A.P.
• Format: Article
• Language: English
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2022.139556

•Mg2NiH4 film growth on a Ni plate from reaction of MgH2 powder with H2 gas.•Film growth occurs in H2 pressure higher than equilibrium for both Mg2NiH4 and MgH2.•Location and mechanism of the film growth reaction are proposed.•Luminescence with quanta energy higher than the band gap of Mg2NiH4 was registered. We studied the synthesis reaction of Mg2NiH4 hydride films when a nickel plate and magnesium hydride powder interacted in the presence of hydrogen at 450 °C. The hydrogen pressure (>6 MPa) was higher than the synthesis equilibrium pressure for both Mg2NiH4 and MgH2 hydrides. Film examination with scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and thermal desorption spectroscopy methods revealed that a dense polycrystalline film of Mg2NiH4 hydride grows on a thin (0.9 μm) underlayer of intermetallic alloy MgNi2. The synthesis time variation made it possible to create Mg2NiH4 films with a width of 0.2 to 4 μm. Based on analysis of the growth kinetics, the crystal structure of the material, and energies of chemical bonds between atoms, we show that the interface between MgNi2 and Mg2NiH4 is the most probable location of the growth reaction. We have obtained cathode luminescence spectra of the Mg2NiH4 hydride film. Mg2NiH4 is found to be an indirect gap semiconductor with a gap value of ∼1.6 eV. However, luminescence with quanta energy higher than the band gap is registered. We associate this fact with Van Hove singularities in the Mg2NiH4 density of states.